1. Field of the Invention
This invention relates to a head drive system wherein a head is protected by differentiating a time interval of energization thereof between a normal operating time and an abnormal operating time.
2. Description of the Prior Art
According to conventional techniques, the circuit configuration for effecting energization of a head is like that shown in FIG. 1(a), wherein response to a pulse signal given from a CPU 1 a one-shot generating circuit 2 is started to generate a one-shot pulse by which a head 3 is energized only during the time interval corresponding to the duration thereof. The timing of the foregoing operation is as shown in FIG. 2(a), in which during the ON time of data .circle.1 , on the basis of a pulse .circle.2 a signal .circle.3 is generated by the one-shot generating circuit 2, and within the time interval corresponding to the pulse duration, the energization of the head 3 is effected ( .circle.4 ). Thus, even if trouble occurs at moment t.sub.1 and is detected by a mechanical trouble detector 4, the time interval of energization of the head does not differ between the normal operating time and the abnormal operating time.
Further, according to the prior art, the energization of the head is sometimes effected undesirably when the CPU runs uncontrollably (FIG. 4(b)).
The conventional system operates in such a manner as is illustrated in the timing chart of FIG. 2(a), and still after mechanical trouble is detected (at moment t.sub.1) during the energization of the head, the head can be energized. That is, the time interval of energization is identical between the normal operating time and the abnormal operating time.
Further, when the CPU runs uncontrollably, individual pulses given from the CPU create ONs and OFFs at random, and the energization of the head continues beyond the timing of each pulse; thus, an undesirable current flows through the head(see .circle.4 in FIG. 4(b)).